1. Field of the Invention
The invention generally relates to systems and methods for purification of water and, more particularly, relates to transportable self-contained water purification systems which require external supplies of fuel for powering an on-board electric power generator and a high pressure reverse osmosis pump, but which are otherwise self-contained, internally generating from the ambient air and the water being treated all other resources necessary for treatment of the water.
2. Description of the Related Art
Water covers more than two-thirds of the earth's surface. Nevertheless, there are many areas throughout the earth where water is scarce or where water, even if available, is not potable. Potable water is water that is suitable for humans and animals to drink and which meets minimum quality standards that may apply.
A great amount of the water on earth is brackish or sea water. Brackish and sea waters are typically not suitable for human and animal consumption because the waters contain salts and sediments which may be harmful. In addition, brackish and sea waters are often unsuitable for other desired uses.
In addition to brackish and sea water, so-called "fresh" water may also be unsuitable for use in certain circumstances. "Fresh" water may be unsuitable if it is polluted or contains certain bacteria or other microorganisms. For these and other reasons, waters found in many locations are not suitable for drinking or other desired uses.
As is generally known, water may be found in pools at the earth's surface or within the subsurface strata.
Surface water may be contaminated by events occurring at the surface. Subsurface water may be polluted by substances seeping through the earth's strata to enter formations containing the water. In any event, both surface water and water obtained from subsurface strata may require treatment prior to consumption and other use by humans and animals.
A number of water treatment systems and methods have been previously developed. Those water treatment systems and methods have sought to treat waters, either surface or subsurface, to make the waters potable. For treatment of large amounts of water, such as to supply cities and towns, large-scale water treatment facilities are generally necessary. These facilities typically include numerous tanks, large pumps, filtration apparatus, and chemical treating facilities. For smaller-scale water treatment, a variety of apparatus and methods are known. Those apparatus and methods typically include combinations of filters for filtration and chemicals for chemical treatment.
There have been earlier attempts to develop a transportable, self-contained water purification system capable of treating and supplying significantly large quantities of potable water. Those prior systems and methods have not been satisfactory, however, for many water treatment applications. For example, some of the systems and methods have been designed to treat only so-called "fresh" water. Those systems have generally treated the "fresh" water by filtration and addition of chemical disinfectants. The filtration serves to remove particulate matters from the water and the chemical disinfectants serve to render the water microbiologically suitable. Those systems and methods for treating "fresh" water typically have not served to remove dissolved substances in the water, for example, salts, which are found in brackish and sea waters.
Attempts have previously been made to develop transportable, self-contained water purification systems and methods for treating brackish and sea water and other waters containing dissolved substances. Those attempts have employed various chemicals and filter processes to prepare the water for a separate treatment process known as reverse osmosis. Reverse osmosis is the separation of solutes from a solution by causing the solvent to float through a membrane at pressures higher than the normal osmotic pressure. This is possible because of the phenomenon of osmosis. In osmosis, a solvent diffuses through a semi-permeable membrane from an area of greater osmotic pressure (i.e., greater concentration of dissolved substance) to an area of lower osmotic pressure (i.e., lesser concentration of dissolved substance). In reverse osmosis, the solvent diffuses through a membrane filter leaving dissolved substances, such as salts and other contaminants, behind.
Those prior technology water treatment systems and methods employing reverse osmosis have several limitations. For instance, those systems and methods have had limited throughput capacity and limited range of treatable input water quality. In addition, those systems and methods have required input of various consumable chemicals and apparatus to the systems and methods, as well as consumable resources for power generation, such as petroleum fuel. Often, these inputs are relatively quickly consumed by the systems and methods during operation and must be continuously or regularly added.
Even further, certain of those prior systems and methods employing reverse osmosis have been limited by requiring particular care in operations because toxic by-products are generated. Those toxic by-products, once generated in the operations, are not easily removed from the systems. Even if removed, those by-products present handling and disposal problems. As can be readily understood and appreciated, a system and method for water treatment which overcomes the limitations and problems of the prior technology and which is also transportable and self-contained would be a significant advantage in the art.
More particularly with respect to toxic by-product generation by the prior systems and methods, the prior technology portable water purification units have employed chlorine for pre- and post-oxidation/disinfection. The use of chlorine as a pre-oxidant (i.e., employed prior to filtration) causes formation of trihalomethanes, which are known carcinogens. Once formed, trihalomethanes are very difficult to remove from water being treated. Prevention of trihalomethane formation, rather than removal, then, is most desirable.
In the prior technology, ozone has sometimes been employed, rather than chlorine, as a pre-oxidant to avoid the problem of trihalomethane formation. Ozone use does not result in trihalomethane formation, but large concentrations of ozone are necessary to accomplish the intense oxidation necessary for water treatment. These large concentrations of ozone cannot be generated by the typical systems and methods, so it has been necessary to supply ozone to those systems and methods from an external source. Ozone availability can be limited or non-existent in many locales.
Also more particularly with respect to external resources required by the prior systems and methods, the prior transportable water purification systems and methods have typically used small, disposable cartridge filters for removal of particulates in the water being treated. Those filters have generally been capable of removing only particulates down to particular sizes for which the filter was designed. In use, filters designed for removal of only larger particulates may be used longer than filters designed for removal of smaller particulates. This is the case because filters designed for removal of larger particulates allow many small particles to pass and the filters do not quickly become clogged. On the other hand, filters designed for removal of smaller particulates pass fewer particles, thus, retaining more. The filters designed for removal of smaller particulates, therefore, tend to have short life-spans, becoming clogged quickly because of the greater number of particulates filtered by those filters from water being treated. Typically, the prior technology filters have been disposed of after use and have not been cleanable and reusable.
Further regarding filters of the prior technology transportable water treatment systems and methods, those systems and methods have in rare instances employed granular activated carbon filter media (GAC). Those that have employed GAC have been small cartridge-style filters. Those filters have not been cleanable and were necessarily disposed of and replaced after a period of use. Further in the prior art systems and methods, much of the adsorptive capacity of GAC filters, when employed, has been spent in removal of chlorine pre-oxidizer, rather than removal of matter from water being treated.
There are at least two known prior technology transportable systems for water purification on a significant scale. One of those systems, referred to in the trade as the "global water system LS3," has the disadvantage of not being useable in treating water containing high total dissolved solids (TDS) (e.g., brackish and sea waters contain high TDS). In addition, that system uses chlorine as a pre-oxidant, thus, resulting in trihalomethane formation and ensuing problems therewith. Further in that system, manual adjustment of chlorine dosage is required which gives variable treatment results and may be subject to human error. That system further includes only a single, non-reusable filter train which must be periodically replaced, and the replacement requires shutdown of the entire system.
The second known, prior technology portable water purification system is used by the U.S. Army and is called the "ROWPU" (for reverse osmosis water purification unit). This system requires addition of a coagulant aid for aiding removal of fine particles and colloids. This coagulant aid is consumed in the system and so must be continuously, or at least regularly, added to the system by an operator. The operator's involvement may lead to variable results, and there is the possibility of human error. Even further, the system requires addition of a scale inhibitor that is also consumed by the system. The system includes a single-stage cartridge filter that is non-reusable. The filter is not satisfactory for many applications, as it will pass viruses, giardia, cryptosporidium, and other bacteria. The system further employs reverse osmosis membranes that foul and must be replaced, and requires addition of residual disinfectant that is consumable and must be added or generated at the system site.
The present invention overcomes the problems of the prior technology water treatment systems and methods and, particularly, the transportable systems and methods previously available. In addition to overcoming the problems of the prior technology systems and methods, the present invention provides numerous additional features not found in the prior technology and improvements over a number of aspects of the prior technology. As will be understood and appreciated by those skilled in the art, the invention is a significant improvement in the technology and provides the herein described advantages and improvements, and many others.